Conventional GM Powerglide servos are not well-supported and the return springs do not function properly, both leading causes of band failure. Sonnax supported servo master kit 28821-20K is an all-in-one kit that eliminates piston binding and includes a race-calibrated spring to counteract the pin bias effect.
At high apply pressures or with a worn servo pin bore, the servo piston is side-loaded in the case, causing friction and binding of the piston. The supported pin design of this Sonnax kit eliminates friction caused by side-loading and ensures the servo piston will apply and release without binding.
"Mystery" band failures are a common result of aftermarket servo return springs and weak OE springs prone to collapse that do not reliably release the servo. The Sonnax spring in this kit is race-calibrated to ensure consistent servo function for longer band life and a cooler transmission. The spring's higher seat pressure helps ensure full servo release, but also features a lower spring rate to prevent excessive release force in the apply position.

Unique cover and pin combination eliminates piston binding that causes unexplained band failure
Race-calibrated spring counteracts pin bias effect up to 275 psi
Dual PTFE seal rings for better seal and low friction
OE apply area
Low-profile design ensures adequate clearance
6061 Anodized billet aluminum cover

More From This Category

PHC Clutch Clutch Alignment Tool, For BedFor Ford TK Truck Range 318ci, 6V53 GM ERV6, 1/70-12/76 1970-1976, Each

PHC Clutch Clutch Alignment Tool, For BedFor Ford TK Truck Range 318ci, 6V53 GM ERV6, 1/70-12/76 1970-1976, Each

$7.29

Motive Gear Differential Master Bearing Kit, Timken, For CHEVROLET G30 1984–1991, Kit

Motive Gear Differential Master Bearing Kit, Timken, For CHEVROLET G30 1984–1991, Kit

$332.72

PHC Clutch Bearing, Release, For Nissan 1000 1.0 Ltr, A10 B10, 4 Speed, 9/66-12/70 1966-1970, Each

PHC Clutch Bearing, Release, For Nissan 1000 1.0 Ltr, A10 B10, 4 Speed, 9/66-12/70 1966-1970, Each

$32.67

Motive Gear Axle Shaft, 1541 Manganese, 5x5 in. Bolt Pattern, 34.813 in. Length, 28SPL, For CHEVROLET ASTRO 1990–2002, Each

Motive Gear Axle Shaft, 1541 Manganese, 5x5 in. Bolt Pattern, 34.813 in. Length, 28SPL, For CHEVROLET ASTRO 1990–2002, Each

$201.81

Motive Gear Axle Shaft, 1541 Manganese, 5x4.75 in. Bolt Pattern, 29.625 in. Length, 31SPL, ForD BRONCO 1966–1975, Each

Motive Gear Axle Shaft, 1541 Manganese, 5x4.75 in. Bolt Pattern, 29.625 in. Length, 31SPL, ForD BRONCO 1966–1975, Each

$389.25